[DMN Designer] Copy of a imported node shouldn't have a prefix

This issue is related to two features of DMN editor.

• Copy and paste diagram node
• Nodes of imported model

If user imported another DMN model into his DMN model, he can use imported nodes in his diagram. They can be easily distinguished by prefix of the imported model. The issue is if we copy and paste such imported node. Created copy has same name as the original node. It is issue because the original-imported one can not be edited while the copy can be edited. Due to the same names it can be confusing why one node can not be edited and the second can be edited.